#devonion

Amphibian crustacea

Though the genus dates back to some 350 million years ago in the Devonian, the rare British species of tadpole shrimp combine an unusual lifestyle with being unchanged over the last 220 million years ( since sometime in the mid Triassic, making it one of our globes oldest extant species). Triops cancriformis can survive for decades as cycsts, blown around by the winds until they encounter water again and return for a brief burst of life, laying eggs for the next generation.

They grow to maturity in a mere 2-3 weeks, allowing them to take advantage of very short lived pools of water. Its growth rate is enhanced by the fact that it will eat almost any kind of organic matter and chew through 40 percent of its body weight daily. Another survival advantage is that short lived ponds are often too ephemeral to support populations of larger predators such as fish. Their maximum size is around 11cm (plus tail), and they can live in brackish or fresh water.

Since the eggs can survive a long time, each batch has the potential to grow in different places in different years, helping the species to widely spread, ensuring its survival. Some hatch the next year if water is present, but others remain in stasis (known as diapause), drying up and going into hibernation. The longest recorded period is 27 years, and they survive desiccation, wind transport, extreme temperatures and being eaten and excreted by other animals.

Other species live in America, across much of Europe, Russia and the Middle East. In Britain they remain endangered, since many temporary ponds have been drained over the last few centuries as useless, thus destroying their habitat, and invasive species are also proving a threat. Only 2 sites are known, in the new Forest and the Solway firth.

Back in the days of Pangea, large chunks of our world were howling deserts lying deep in the supercontinent's interior. In these circumstances evolving a survival strategy to take advantage of brief burst of liveability when a pond appears after a burst of rain or flash flood amidst a background of harsh and arid times makes a lot of sense. What a tough, charming and enduring creature, looking like a cross between a trilobite and horseshoe crab.

Loz

Image credit: Adrian Davies/National Parks